The present invention relates to the application of thixotropic gels to fibers and more particularly to apparatus for applying thixotropic gels to glass fibers at forming.
It has been proposed to apply existing coating materials to glass fibers at forming as thixotropic gels. Normal thixotropic gels are gels at ambient conditions under non-shear conditions. When a shear stress of sufficient magnitude is applied to these gels, they take on the viscosity of solutions; when the shear stress is removed, they revert to gel.
When a thixotropic gel is applied to a pad-type applicator by hand and the fibers pulled through the pad, a suitable coating can be produced, but the supply of material on the pad cannot be replenished in the usual manner and no known apparatus is suitable. When a belt-type applicator, as for example that shown in the Brasitigam U.S. Pat. No. 2,873,718, is used for applying the gel to the fibers, an uneven coating is produced with some portion of the fibers being left uncoated. When uncoated portions of the fibers are drawn together to form a strand the strand can break. In addition, gel collects at various points of the equipment and is either carried along with the fibers to the package as globs, or drops to the floor of the surrounding area. Air bubbles are dispersed throughout the gel and are carried to the glass fibers, with the result that whenever the fibers are drawn through an air bubble, the fibers remain uncoated and subsequently break. When an applicator such as shown in the Ewing U.S. Pat. No. 3,244,143 is used, air bubbles are also carried along with the gel to the glass fibers with the result that the fibers remain uncoated and subsequently break. The thixotropic gel applicator as shown in the Hill et al U.S. Pat. No. 3,498,262 has been used to apply gel to glass fibers. However, there can be problems with this type applicator such as, for example, thixotropic gel material which is not applied to the glass strands can be sheared between the applicator roll and the lower portion of the applicator block assembly. This can result in clogging of the size applicator and non-uniform distribution of gel on the applicator roll.